This is a career grant application for Dr. Soto-Gutierrez;an M.D.;Ph.D. who specializes in cell therapies and liver diseases. Dr. Soto-Gutierrez has recently developed novel methods of differentiating stem cells into liver cells, and his interests have shifted to application of such tools to organ engineering. To establish himself as an independent researcher in the field of organ engineering, Dr. Soto-Gutierrez submits this fiveyear career development plan under the sponsorship of Dr. Martin Yarmush, the Helen Andrus Benedict Professor of Surgery and Bioengineering at Harvard Medical School and the director of the Center for Engineering in Medicine at the Massachusetts General Hospital, which includes i) intensive hand-on training in organ engineering, isolated liver-matrices perfusion and stem cell differentiation, ii)academic courses and seminars, and iii) guidance of a select advisory committee. Our long-term goals are to develop a natural hepatic platform for complete and stable maturation of stemderived liver cells and to engineer functional liver grafts. The objectives of the proposed study are to develop an extracorporeal perfusion liver-matrix-scaffold system for repopulation and hepatic maturation of stem liver-derived cells, and investigate its employment for the creation of auxiliary liver grafts for transplantation in patients with impaired hepatic function. The central hypothesis to be tested here is that the decellularized natural liver scaffold, obtained from discarded livers, can be extensively repopulated and can provide an adequate maturation environment for stem derived liver cells, and this organ culture system can be employed to engineer metabolic functional liver grafts for transplantation. The rationale of the study is that ischemically damaged, untransplantable organs are available in numbers that far surpass the current demand, and they present an ideal platform for delivery for stem cell-based therapies. The work described here is expected to i) establish a protocol for recellularization and engraftment of hepatocyes in decellularized matrices, ii) generate a repopulation and maturation system for stem cell-derived hepatocytes, and iii) develop a novel method of liver graft engineering for transplantation as auxiliary liver support in hepatic diseases. The results of this work will also have a positive impact by establishing the basis and platform for future sophisticated organ engineering techniques that incorporates several different cell types, can be applied to other organs and may lead to development of entire organs in vitro.